全文获取类型
收费全文 | 8204篇 |
免费 | 790篇 |
出版年
2023年 | 55篇 |
2022年 | 129篇 |
2021年 | 249篇 |
2020年 | 149篇 |
2019年 | 187篇 |
2018年 | 216篇 |
2017年 | 165篇 |
2016年 | 272篇 |
2015年 | 427篇 |
2014年 | 512篇 |
2013年 | 493篇 |
2012年 | 704篇 |
2011年 | 673篇 |
2010年 | 413篇 |
2009年 | 321篇 |
2008年 | 464篇 |
2007年 | 427篇 |
2006年 | 398篇 |
2005年 | 308篇 |
2004年 | 295篇 |
2003年 | 259篇 |
2002年 | 220篇 |
2001年 | 124篇 |
2000年 | 110篇 |
1999年 | 95篇 |
1998年 | 60篇 |
1997年 | 43篇 |
1996年 | 30篇 |
1995年 | 32篇 |
1994年 | 42篇 |
1993年 | 42篇 |
1992年 | 62篇 |
1991年 | 51篇 |
1990年 | 53篇 |
1989年 | 67篇 |
1988年 | 38篇 |
1987年 | 67篇 |
1986年 | 54篇 |
1985年 | 65篇 |
1984年 | 49篇 |
1983年 | 50篇 |
1982年 | 39篇 |
1981年 | 30篇 |
1980年 | 44篇 |
1979年 | 60篇 |
1977年 | 26篇 |
1976年 | 31篇 |
1975年 | 33篇 |
1974年 | 40篇 |
1972年 | 26篇 |
排序方式: 共有8994条查询结果,搜索用时 38 毫秒
141.
Summary The morphogenesis of the juxtaglomerular apparatus and peripolar cells was studied in the metanephros of fetal sheep (from 24 to 147 days of gestation) using light and electron microscopy. The first juxtaglomerular apparatus was detected at 45 days of gestation, following constriction of the edges of Bowman's capsule and formation of the vascular pole of the renal corpuscle. Mesenchymal cells gave rise to lacis cells and to smooth muscle and epithelioid cells of the juxtaglomerular arterioles. Epithelioid cells developed only sparse cytoplasmic granulation, first detectable at 92 days. The macula densa developed from tubular cells at the junction of the middle and upper limbs of the S-shaped body of the developing nephron. Peripolar cells arose from epithelial cells in the lower limb of the S-shaped body, at the constricting edges of Bowman's capsule, and formed a cuff around the origin of the glomerular tuft. Cytoplasmic granules were first detected in peripolar cells at 53 days, and remained more prominent than epithelioid cell granulation throughout gestation. 相似文献
142.
143.
A sycamore cell wall polysaccharide and a chemically related tomato leaf polysaccharide possess similar proteinase inhibitor-inducing activities 总被引:14,自引:7,他引:7 下载免费PDF全文
A large pectic polysaccharide, called rhamnogalacturonan I, that is solubilized by a fungal endo-α-1,4-polygalacturonase from the purified walls of suspension-cultured sycamore cells possesses proteinase inhibitor-inducing activity similar to that of the proteinase inhibitor-inducing factor, a pectic-like oligosaccharide fraction isolated from tomato leaves. This suggests that the proteinase inhibitor-inducing activity resides in particular polysaccharide fragments which can be released when plant cell walls are exposed to appropriate enzyme degradation as a result of either wounding or pest attack. 相似文献
144.
Quantification of surfactant phospholipids in the dog lung 总被引:1,自引:0,他引:1
S F Ryan S A Hashim G Cernansky C R Barrett A L Bell D F Liau 《Journal of lipid research》1980,21(8):1004-1014
We quantified total phospholipid (PL), total and disaturated phosphatidylcholine (PC and DSPC), phosphatidylglycerol (PG), and total protein in alveolar washings and lung tissue in 22 dog lungs. Quantitative recovery of alveolar material and assessment of its possible contamination by blood lipids were important determinants of methodology. To remove blood, the vessels of half the lungs were perfused with a fluorocarbon emulsion before lavage. The volume of blood removed by perfusion and the quantity and fatty acid patterns of its whole blood and plasma PL and PC were determined. Washings of unperfused lungs contained means of 21% more PL and 24% more PC than those of perfused lungs. Although this excess could be accounted for by the PL and PC in pulmonary blood, the hemoglobin and total protein content of washings and their PC fatty acid patterns indicated that blood lipids were not a major source of the excess lipid in washings of unperfused lungs. Using more recent morphometric estimates rather than the indirect ones previously used by others, the quantity of alveolar DSPC (1 mg/g lung) is calculated to be 1.8 times the amount necessary to form a packed monolayer on the internal surface of the lung at functional residual capacity. 相似文献
145.
146.
P G Casola F Chan P M Macdonald S Ryan W C McMurray F Possmayer 《Biochemical and biophysical research communications》1980,96(3):1209-1215
The enzymes responsible for the biosynthesis of phosphatidylglycerol, CTP:phosphatidate cytidylyltransferase, CDP-diacylglycerol: glycerophosphate phosphatidyltransferase and phosphatidylglycerophosphate phosphatase demonstrated a coordinate increase in activity in fetal rat lung at term when the demand for pulmonary surfactant increases. The activity of CTP:cholinephosphate cytidylyltransferase, the enzyme responsible for CDP-choline production also increased in the perinatal period. The activity of cholinephosphate cytidylyltransferase in fetal and neonatal cytosol was stimulated by the addition of phosphatidylglycerol but no effect was noted with cytosol from adult lung. These results are consistent with the suggestion that the activity of cholinephosphate cytidylyltransferase, a potential rate-determining enzyme in pulmonary phosphatidylcholine synthesis, may be regulated in the perinatal period both through an activation by phosphatidylglycerol and by an increase in total enzyme units. 相似文献
147.
Jeffrey K. Yao Steve C.S. Chang Robert J. Ryan Peter James Dyck 《Biochemical and biophysical research communications》1980,95(2):738-744
The unique features of pig ovarian follicular fluids, i.e., presence of high density lipoprotein (HDL) only and lecithin: cholesterol acyltransferase (EC 2.3.1.43; LCAT) activity, provides a good model to study the effect of serum lipoproteins and serum albumin on the LCAT reaction. cholesterol esterification is enhanced when very low density lipoprotein (VLDL) and low density lipoprotein (LDL) fractions are added, but is inhibited when one or the other of these lipoproteins is absent. High concentrations of HDL2 result in decreased activation which can be compensated for by the addition of the VLDL-LDL mixture. These findings suggest that the rate of cholesterol esterification in ovarian follicular fluid may be enhanced by providing the exogenous VLDL and LDL as the recipients of HDL-cholesteryl ester. The inhibition of LCAT activity caused by free fatty acid and lysophosphatidylcholine can be partially reversed by the addition of serum albumin, suggesting that serum albumin may regulate the LCAT reaction. 相似文献
148.
149.
150.